Since the 1970s, a number of changes have dramatically altered the context in which youth and adults become parents. The proposed study addresses the implications of these changes for the transition to biological parenthood among U.S. adolescents and adults, with a particular focus on early fatherhood and its circumstances. Toward this end, we plan on answering these questions: How do social policies, in addition to economic and family-demographic factors, influence the timing and circumstances of biological parenthood? What influence do these factors have on behaviors that condition the timing and circumstances of biological parenthood, specifically, union formation, sexual behavior, and reproductive behavior? How does the influence of different factors on biological parenthood differ by historical period, race, and socioeconomic status? To answer these questions, we will use data from several nationally representative surveys. We also plan to utilize a data set to be developed by the P01 core that will include economic, family-demographic, and policy variables at the state, county, and neighborhood levels for the years during which sample members are at risk of becoming a parent. Our models will estimate the effects of variables measured at several levels on the risk of becoming a parent.